1. Field of the Invention
The present invention relates to a method of manufacturing a superconductor having anisotropic conductivity, and more particularly, it relates to a method of manufacturing a superconductor, which can improve its critical current density.
2. Description of the Prior Art
In the case of a superconductor consisting of an alloy or an intermetallic compound, its superconductivity is not influenced by azimuths of crystal axes, i.e., is isotropic. Therefore, it is not necessary to consider the azimuths of the crystal axes but the superconductor can be manufactured by various methods such as a powder sintering method, a melting method and a sputtering method, depending on its use.
In the case of a ceramic superconductor which is mainly manufactured by the powder sintering method or the like, however, its superconductivity varies with the azimuth of the crystal grains forming the same, to have anisotropic conductivity. Thus, it has been recognized that current density of a superconductor cannot be effectively improved unless the same is so manufactured as to orient its crystal axes in a constant direction.
As hereinabove described, a ceramic superconductor of a polycrystalline substance manufactured by a conventional method such as the powder sintering method or the melting method is anisotropic with respect to superconductivity, if the crystal axes thereof are not oriented in a constant direction. When a current is fed to such a ceramic superconductor of a polycrystalline substance, for example, loss is caused by anisotropy between crystals, to prevent flow of a large current. Therefore, such a superconductor is manufactured by performing heat treatment for monocrystallizing the same, or by growing a thin film the crystal axes of which are oriented in a constant direction, to improve the current density of the superconductor. In such a method, however, much labor is required in order to manufacture superconductor materials of high volume of in bulk.
A superconductor manufactured by the melting method or the powder sintering method generally consists of a polycrystalline substance, the crystals of which are randomly arranged. Therefore, heat treatment is repeated on the polycrystalline substance to orient its crystal axes in a constant direction or temperature treatment is performed with a temperature gradient, thereby to bring the entire polycrystalline substance into a completely superconducting state. However, the degree of superconductivity of such products varies, and hence much time and labor are required in order to manufacture uniform superconductors.